Field of the Invention
The present invention relates to image forming apparatuses driven by optical scanning apparatuses that scan using multiple beams of light emitted from multiple light sources driven by multiple ICs.
Description of the Related Art
Japanese Patent Laid-Open No. 2011-173412 proposes an exposure apparatus (optical scanning apparatus) capable of simultaneously driving a total of eight lasers by using two laser control apparatuses (drivers) that are each capable of controlling four lasers. According to this optical scanning apparatus, eight primary scanning lines can be drawn simultaneously by the eight lasers, and thus the image forming apparatus can achieve higher speeds.
Meanwhile, a driver IC manufactured by integrating driving circuits can be used as a shared component in a high-speed printer, which uses the eight lasers, and a mid-speed printer, which uses four lasers. Using the same component among printers having different grades enables more of the same driver ICs to be manufactured, which leads to a reduction in costs.
However, even if multiple driver ICs that are identical components are used, scanning unevenness (exposure unevenness) can arise due to increases and decreases in the temperatures of the respective driver ICs. In other words, if the driver ICs used to form multiple primary scanning lines arranged in a secondary scanning direction (a rotation direction of the photosensitive member) are different, the exposure amounts of the primary scanning lines will vary depending on the driver ICs that are used. Specifically, different image data supplied to the multiple driver ICs, and the total level of current output for driving the lasers will also differ, resulting in different amounts of heat being produced by the respective driver ICs. In image forming apparatuses provided with optical scanning apparatuses, exposure unevenness leads to unevenness in the darkness, and this phenomenon can be particularly marked in images where there is a combination of horizontal stripes and halftones.
Japanese Patent Laid-Open No. 2007-329429 does disclose finding a driving current that achieves a constant light emission amount, taking into consideration the influence of temperature among multiple light-emitting elements provided in a surface emitting laser. However, Japanese Patent Laid-Open No. 2007-329429 does not focus on differences in amounts of heat produced among multiple driving ICs.